Micropolar Electromagnetic Fluids: Theory and Simulation
Open AccessMolecular dynamics (MD) has shown that molecular spin makes a fluid act significantly different at the micro/nano scale than at the macroscale. Experimental data also imply that the classical Navier-Stokes equations are incapable of explaining several kinds of microscale transport phenomena. Though Molecular Dynamics simulation allows the observation of molecular spin, the computation cost is unaffordable. To tackle such problems with consideration of computational efficiency, one should resort to Microcontinuum Theory.This dissertation is divided two main parts: theory and simulation. In the theoretical part, the balance laws are provided and the constitutive equations for Micropolar electromagnetic fluids are derived through two approaches: (1) Wang's representation theorem and (2) Onsager's theory. The constitutive equations of fluids are required to satisfy the axiom of objectivity. The axiom of objectivity allows the utilization of Wang's representation theorem. The constitutive equations are therefore obtained through Wang's representation theorem and later linearized for practical applications. The linear constitutive equations can be also obtained from Onsager's theory. These two sets of constitutive equations are identical. One new parameter for fluids, the curl of gyration, is found to characterize electric current. The nonlinear Onsager's theory for constitutive equations was originally derived by Edelen. It is now further extended for fluids through integration with Wang's representation. The connections to Couple Stress Theory and Navier-Stokes equations are made from Micropolar Theory. In the simulation part, a second order Finite Difference (FD) method is integrated with the time-centered split method (TCSM) and is successfully developed for an incompressible fluid. A higher-order Spectral Difference (SD) method is further developed for compressible Micropolar fluid problems. The analytical and exact solutions, including velocity, gyration and temperature, for incompressible and compressible plane Couette flow and for incompressible Hagen-Poiseuille flow, are given. These analytical and exact solutions are used to verify the order of numerical accuracy for the aforementioned numerical solvers. Based on numerical results, the physical meanings of material coefficients are clearly described. Flows past a cylinder with and without imposed transverse uniform magnetic field are also studied. Imposition of a magnetic field is demonstrated as an effective approach for flow control.
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